The so-called new screw is compared to a conventional f […]
The so-called new screw is compared to a conventional full-thread three-stage screw. The new type of screw has many features in principle and structure design. They are developed on the basis of conventional full-thread three-stage screw and have been widely used.
The so-called new screw mainly refers to:
4.1 Problems with conventional full-thread three-stage screw
1. Low melting efficiency, plasticizing and mixing (dyeing, filling) unevenness 1) Heat transfer route
According to the theory of melting, there are two heat sources for solid bed melting:
One is the external heat from the heater.
The first is the shear heat that occurs in the melt film.
The latter is the main one. The maximum melting efficiency can be obtained if the solid bed can always be brought into contact with the wall of the cartridge in the largest area before it disappears.
2) The solid bed is narrowed, the heat transfer area is reduced, the melting efficiency is low, and the extrusion amount is not high. In the conventional three-stage screw, the solid bed and the molten pool in the melting section coexist in one screw groove, and the molten pool is continuously widened, and the solid bed is widened. The tape is gradually narrowed, thereby reducing the contact area between the solid bed and the wall of the barrel, reducing the heat directly transferred to the solid bed by the wall of the barrel, and reducing the melting efficiency, resulting in a low extrusion amount.
3) The solid bed is easily broken, the solid fragments are slow to transfer, the shearing force is small, and it is not easy to melt a. The solid bed is easily broken: in the conventional three-stage screw, when the solid bed width is reduced to 10% of its initial width. Its physical properties are extremely unstable, and the solid bed is easily disintegrated to form solid fragments.
b. The solid debris is surrounded by the melt, and the external heat cannot be directly obtained. The slow heat transfer solid debris is mixed into the molten plastic, surrounded by the melt, and cannot directly contact the wall of the cylinder to obtain the heat of the external heater. Heat can only be obtained from the melt surrounding them. Since the heat transfer properties of the molten polymer are poor, it will be difficult and very slow to completely melt the fragments.
c. The solid debris floating in the melt is subjected to little shear force, and it is difficult to obtain heat from the shear. The solid debris is surrounded by the melt, which is in a floating state, and substantially no shear occurs.